The University of Medical Sciences in Teheran gave men 10 mg boron every day for a week with their breakfast. The result was that their free testosterone levels rose by almost thirty percent and their estradiol went down by forty percent.
Sources:J Trace Elem Med Biol. 2011 Jan;25(1):54-8.
Comparative Effects Of Daily And Weekly Boron Supplementation On Plasma Steroid Hormones And Proinflammatory Cytokines
Notes for this study:
10mg Boron for 6 days was able to reduce estrogen without influencing total androgen status, but increasing free testosterone (possibly via a reduction in SHBG) in 6 apparently healthy average male adults